Effects of polymer hardness on the abrasive wear resistance of thick organic offshore coatings

For the first time, effects of polymer hardness on the abrasive wear resistance of organic coatings, designed for the corrosion protection of offshore wind power structures, are investigated at varying normal forces. The tests are performed with a specially designed Taber abrasion machine. The results reveal statistically significant effects of the polymer material Vickers hardness on the coating resistance against abrasive wear. With respect to the generic polymer type, the following ranking of the abrasive wear resistance is estimated: epoxy > polysiloxane > polyurethane. Thus, the most frequently applied top coat material (polyurethane) exhibits the lowest abrasive wear resistance and may not be capable to protect the underlaying epoxy-based intermediate coats. Polysiloxane would provide a longer protection against abrasive wear. The dominant material removal modes in all polymers are microcutting and microfracturing, whereby the former mode is dominant at lower normal forces, and the latter mode is dominant at higher normal forces. The power exponent of the classical power relationship V-A proportional to H-p(n) depends on the mixture of the associated removal modes. The authors introduce a new transition parameter in order to rank the associated individual material removal processes. Based on an empirical-mathematical model, a two-parameter Weibull distribution function is derived, which links the transition parameter to the applied normal force. A two-dimensional graph (nomogram) is designed, where the different material removal modes are situated as functions of normal force and transition parameter.